Memtest reports errors - sometimes, wierd problem

[LMRig]

i7 6700k
Maximus VIII Extreme
G.Skill Tridentz 2x8GB 4000MHz

Hello, yesterday my PC crashed with BSOD when I ran high usage program (benchmark) or game. So I tested RAM with Memtest on USB FD.

I got more than 1000 errors in test 6. So I downclocked RAM to 3866 and Memtest was without errors, one stick had errors and one didn't boot with 4000MHz.
Today I tested it again. Used XMP for 4000Mhz, booted ok, benchmarks are ok but... memtest shows errors again but only around 40.


Attaching log with yesterday errors and today...

[David (PassMark)]

Doesn't seem that weird.
Your RAM doesn't run reliably at 4000Mhz.
Variation in the number of errors from one day to the next might be due to external factors. Temperature, EMI, etc..

[LMRig]

Mmm, ok, thank you for information, so I have to RMA.

[David (PassMark)]

4000Mhz clock speed is really high. For these type of speeds I would be thinking you would want to make sure your motherboard has been qualified to work with whatever RAM you select.

Note also that for most applications the real world difference between 3866Mhz and 4000Mhz is really tiny. Maybe just 3%, which isn't large enough to notice, unless you are doing some precise benchmarking.